Primary

compensation

Greater cognitive activity doesn’t appear to prevent Alzheimer’s brain damage, but is associated with more neurons in the prefrontal lobe, as well as other gender-specific benefits.

Data from the very large and long-running Cognitive Function and Ageing Study, a U.K. study involving 13,004 older adults (65+), from which 329 brains are now available for analysis, has found that cognitive lifestyle score (CLS) had no effect on Alzheimer’s pathology. Characteristics typical of Alzheimer’s, such as plaques, neurofibrillary tangles, and hippocampal atrophy, were similar in all CLS groups.

However, while cognitive lifestyle may have no effect on the development of Alzheimer's pathology, that is not to say it has no effect on the brain. In men, an active cognitive lifestyle was associated with less microvascular disease. In particular, the high CLS group showed an 80% relative reduction in deep white matter lesions. These associations remained after taking into account cardiovascular risk factors and APOE status.

This association was not found in women. However, women in the high CLS group tended to have greater brain weight.

In both genders, high CLS was associated with greater neuronal density and cortical thickness in Brodmann area 9 in the prefrontal lobe (but not, interestingly, in the hippocampus).

Cognitive lifestyle score is produced from years of education, occupational complexity coded according to social class and socioeconomic grouping, and social engagement based on frequency of contact with relatives, neighbors, and social events.

The findings provide more support for the ‘cognitive reserve’ theory, and shed some light on the mechanism, which appears to be rather different than we imagined. It may be that the changes in the prefrontal lobe (that we expected to see in the hippocampus) are a sign that greater cognitive activity helps you develop compensatory networks, rather than building up established ones. This would be consistent with research suggesting that older adults who maintain their cognitive fitness do so by developing new strategies that involve different regions, compensating for failing regions.

In the study, participants pressed buttons in response to the colors of words and random letter strings — only the colors were relevant, not the words themselves. They then completed word fragments. In one condition, they were told to use words from the earlier color task to complete the fragments (a test of explicit memory); in the other, this task wasn’t mentioned (a test of implicit memory).

Older adults showed better implicit than explicit memory and better implicit memory than the younger, while the reverse was true for the younger adults. However, on a further test which required younger participants to engage in a number task simultaneously with the color task, younger adults behaved like older ones.

The findings indicate that shallower and less focused processing goes on during multitasking, and (but not inevitably!) with age. The fact that younger adults behaved like older ones when distracted points to the problem, for which we now have quite a body of evidence: with age, we tend to become more easily distracted.